The present invention relates to a color picture tube apparatus which is used for television sets, computer displays, etc.
A color picture tube having an in-line electron gun at its neck portion is provided with a self-convergence deflection yoke to make three electron beams converge to the same spot on a screen. In actual practice, however, complete convergence cannot always be obtained at all portions on the screen of the color picture tube, even when the self-convergence deflection yoke is used. Misconvergence may occur depending on the design of deflection magnetic fields, variations in assembled components, etc.
In order to correct such misconvergence, a correction coil for generating a magnetic field which corrects misconvergence, and a correction circuit for controlling current flowing through the correction coil are connected to the deflection yoke of a conventional color picture tube.
FIGS. 9 and 10 show schematic views for explaining states of misconvergence in a color picture tube. FIG. 9 shows vertical line (hereinafter is referred to as YH) misconvergence developed at the top and bottom ends of a vertical line displayed at the screen center of a color picture tube. FIG. 10 shows horizontal line (hereinafter referred to as "YV") misconvergence developed at the top and bottom ends of the screen center of a color picture tube.
As means for correcting the YH misconvergence shown in FIG. 9, on the electron gun side of the deflection yoke, two YH misconvergence correction coils used in a pair are disposed above and below the electron gun unit so as to generate four-pole YH correction magnetic fields. With this configuration, currents flowing through the YH misconvergence correction coils are controlled by a YH correction circuit.
As means for correcting the YV misconvergence shown in FIG. 10, YV correction coils are disposed above and below the electron beam unit so as to sandwich it. Furthermore, the YV correction coils are wound so that the same magnetic pole generation portions at the ends of each coil are disposed opposite to each other when currents flow in the YV correction coils. The currents flowing through the YV misconvergence correction coils are controlled by the YV correction circuit in order to correct YV misconvergence.
Two conventional color picture tubes relating to the present invention will be described below.
FIG. 11 shows a YH correction circuit for correcting misconvergence developed at a deflection yoke, disclosed in Japanese Laid-open Patent Application, Publication No. 7-288829. The YH correction circuit shown in FIG. 11 will be described below as a first prior art color picture tube.
As shown in FIG. 11, in a deflection yoke mounted on a color picture tube in accordance with the first prior art, a diode bridge circuit having four diodes D1, D2, D3 and D4 is provided inside a YH correction circuit 100.
Fixed resistors R1, R2 are connected across the input terminals d, e of the diode bridge circuit. Comatic aberration correction coils L1, L2 are connected in series between the YH correction circuit 100 and a vertical deflection coil 101. In addition, YH correction coils L3, L4 are connected between a movable terminal C of a variable resistor VR1 and a connection point of the fixed resistors R1, R2. When the movable terminal C of the variable resistor VR1 is at the electrical center of the range between fixed terminals A, B, the bridge circuit is designed so as not to allow current to flow between the movable terminal C of the variable resistor VR1 and the connection point of the resistors R1, R2.
The first prior art configured as described above has been used to adjust positive and negative misconvergence owing to vertical deflection magnetic fields, thereby to enhance the quality of the color picture tube.
A second prior art color picture tube will be described below. The second prior art is obtained by connecting the deflection yoke of the first prior art to a YH correction circuit and a YV correction circuit in series.
As shown in FIG. 12, a block diagram showing an example of circuit configuration of a conventional correction circuit, a YH correction circuit 16 and a YV correction circuit 17 are used as independent circuits and connected in series in the conventional deflection yoke. Since the correction circuits are connected in series in the deflection yoke, it is important to reduce the resistance value inside each correction circuit or the resistance value of the vertical deflection coil itself in order to prevent loss in the circuit.
In the above-mentioned first prior art, the YH correction coils L3, L4 are connected in series between the movable terminal C of the variable resistor VR1 inside the diode bridge circuit and the connection point between the fixed resistors R1, R2. Therefore, the current flowing through the YH correction coils L3, L4 flows through one of the fixed resistors R1 and R2 at all times, thereby causing a problem of lowering sensitivity.
Furthermore, reducing the resistance values of the correction circuits and the correction coil has a limit in the second prior art. Therefore, it is difficult to attain significant reduction in the resistance values. Moreover, reducing the circuit resistance values of main coils such as the vertical deflection coil is also limited with regard to temperature characteristics and performance characteristics. Therefore, it is also difficult to reduce large resistance values.